The Collaborative International Dictionary of English v.0.48:

Crumbly \Crum"bly\ (-bl[y^]), a.
   Easily crumbled; friable; brittle. "The crumbly soil."
   --Hawthorne.

   Syn: crimp.
        [1913 Webster]

WordNet (r) 3.0 (2006):

crumbly
    adj 1: easily broken into small fragments or reduced to powder;
           "friable sandstone"; "friable carcinomatous tissue";
           "friable curds formed in the stomach";"crumbly cookies"
           [syn: crumbly, friable]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "crumbly":
   breakable, brittle, brittle as glass, cheap-jack, cobwebby,
   crackable, crimp, crisp, crispy, crump, crushable, dainty,
   delicate, delicately weak, effeminate, fissile, flimsy,
   fracturable, fragile, frail, frangible, friable, gimcrack,
   gimcracky, gossamery, jerry, jerry-built, lacerable, light,
   lightweight, namby-pamby, papery, pasteboardy, pulverizable,
   pulverulent, puny, rubbery, scissile, shatterable, shattery,
   shivery, sissified, sleazy, slight, splintery, tacky, triturable,
   unsubstantial, vulnerable, wispy, womanish